Free ASBOG FG/PG Exam Flashcards

In an undeformed sedimentary stack, each bed is older than the one above and younger than the one below. It is the foundation of relative dating but fails where overturning, thrusting, or intrusion has disrupted the original order.

Loose sediment deposits in horizontal layers under gravity, so tilted or folded beds imply post-depositional deformation. Use it to distinguish primary attitude from structural rotation when interpreting a map or outcrop.

A dike, fault, or unconformity that cuts another unit must be younger than what it cuts. This brackets relative ages even when no radiometric date is available.

Fragments inside a rock are older than the rock that contains them: conglomerate clasts predate the matrix, and a xenolith-bearing granite is younger than the xenolith source. The rule is the basis for provenance interpretation.

Fossil assemblages succeed one another in a definite, recognizable order through geologic time, allowing correlation of strata across regions. It is the basis of biostratigraphic zonation and is independent of absolute (numerical) dating.

Eons divide into eras, then periods, epochs, and ages; the Phanerozoic comprises Paleozoic, Mesozoic, and Cenozoic eras. Older rocks are grouped as Precambrian (Hadean, Archean, Proterozoic), which spans most of Earth's history.

Disconformities separate parallel strata; angular unconformities overlie tilted lower beds; nonconformities overlie igneous or metamorphic basement; paraconformities show no visible erosion surface but hide a time gap. Each records a different missing-time mechanism.

A scratch-ordinal scale from 1 (talc) to 10 (diamond) ranking abrasion resistance. It is nonlinear: the absolute jump from 9 to 10 dwarfs the rest, so it identifies minerals but does not measure engineering strength.

Six systems (isometric, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal) are defined by axis lengths and angles; the trigonal subdivision shares hexagonal geometry. System fixes symmetry, cleavage directions, and thin-section optical behavior.

Nesosilicates (isolated tetrahedra, olivine), inosilicates (single and double chains, pyroxenes and amphiboles), phyllosilicates (sheets, micas), and tectosilicates (frameworks, quartz and feldspar) form a polymerization series. More oxygen sharing means higher Si:O ratio and generally lower density.

The discontinuous branch (olivine to pyroxene to amphibole to biotite) and the continuous branch (Ca-rich to Na-rich plagioclase) define crystallization order as magma cools. Early-forming minerals are highest-temperature and least stable at the surface, which is why mafic minerals weather first.

Removing early crystals from a magma changes the residual melt, driving mafic compositions toward intermediate then felsic. A single parent magma can thereby produce a chemically diverse rock suite.

Chlorite, biotite, garnet, staurolite, kyanite, and sillimanite form a progressive pressure-temperature series in metapelites. Their appearance marks isograds that map metamorphic grade; the mineral assemblage, not a single mineral, is the reliable indicator.

The ideal turbidite bed (Ta to Te): graded massive sand, plane-parallel lamination, ripple cross-lamination, upper parallel lamination, and pelagic mud. Partial sequences are common and reflect distance from the source or changing flow concentration.

In a conformable vertical sequence, facies that are laterally adjacent must appear vertically in the same order. It links modern depositional environments to the rock record but fails wherever an unconformity breaks the succession.

A facies is a rock unit defined by lithology, sedimentary structures, fossils, and depositional character; a facies model generalizes facies associations into a predictive depositional reconstruction. Use the model to interpret lateral equivalents, not to force every outcrop into one template.

Sequence boundaries form during relative sea-level fall; transgressive surfaces mark flooding onset; the maximum flooding surface records peak landward shoreline and the condensed section. Systems tracts stack between these surfaces and control reservoir and seal geometry.

Fossils that are widespread, abundant, easily recognized, and restricted to a short time range, enabling correlation of strata across regions. They give relative age, not absolute age; diachronous taxa and reworked specimens can mislead if used uncritically.

First-order streams have no tributaries; two first-orders join to make a second-order, and so on. Drainage density (total channel length divided by basin area) reflects climate, lithology, and infiltration: high density typically signals low permeability or arid conditions.

On a meander bend, the cut bank (outside) erodes where centrifugal force concentrates the fastest flow, while the point bar (inside) accretes where flow slows. Lateral migration widens floodplains and produces oxbow lakes when cutoffs occur.

Till is unsorted, unstratified sediment deposited directly by ice; stratified drift (eskers, kames, outwash) is sorted and bedded by meltwater. The presence of sorting and stratification distinguishes ice-laid from meltwater-laid sediment in the field.

The steepest slope at which loose granular material is stable, typically 30 to 35 degrees for dry sand. Coarse angular grains stand steeper and rounded wet grains slump lower; exceeding the angle triggers sliding.

In the summer active layer over permafrost, meltwater cannot drain through frozen ground, so saturated soil flows downslope on slopes as gentle as 2 to 3 degrees. The resulting lobes and terraces are diagnostic of periglacial mass wasting.

Wind-blown silt (20 to 50 microns) sourced mainly from glacial outwash plains or deserts. Loess is porous, friable, vertically jointed, and fertile, but it is highly erodible and prone to hydrocompaction when first wetted.

Stress is force per unit area applied to a rock; strain is the resulting deformation (length, shape, or volume change). Stress causes strain, but the strain magnitude depends on rock strength, temperature, strain rate, and confining pressure.

Brittle failure (fractures, faults) dominates at low temperature, low confining pressure, and high strain rate; ductile flow (folds, mylonites) dominates at high temperature and confining pressure. The brittle-ductile transition is depth-dependent and shifts with lithology.

Normal faults drop the hanging wall (extension), reverse faults raise it (compression), and strike-slip faults move horizontally (shear). Thrust faults are low-angle reverse faults; the geometric distinction controls slip behavior and seismic style.

The hinge is the line of maximum curvature, the axial plane connects hinges through the fold, and the limbs form the flanks. Fold classification (symmetric, asymmetric, overturned, recumbent, plunging) follows the axial-plane attitude and limb vergence.

Joints are extensional fractures with no visible offset, shears show parallel offset, and faults have measurable displacement. Sheeting joints form parallel to topography from pressure release, unlike columnar cooling joints, which are perpendicular to cooling surfaces.

Mantle convection, ridge push (gravitational sliding from elevated ridges), and slab pull (sinking of dense lithosphere) drive plate motion; slab pull is generally the dominant force. Transform boundaries like the San Andreas connect spreading or subduction segments and take up lateral motion.

Discharge through a porous medium scales with hydraulic conductivity, cross-sectional area, and hydraulic gradient (Q = -K x A x dh/dl). Darcy flux is Q divided by A; actual seepage velocity is Darcy flux divided by effective porosity.

Hydraulic conductivity (K) describes a porous medium and the fluid moving through it under a unit gradient; transmissivity (T = K x saturated thickness) describes the whole aquifer. Use K to compare lithologies and T for aquifer-scale well-yield estimates.

Specific yield is the fraction of total volume that drains by gravity; specific retention is held against gravity, and their sum equals total porosity. Clean sand aquifers have high specific yield, while fine-grained units retain most of their water.

Volume of water released or stored per unit surface area per unit head change. In confined aquifers it reflects compressive storage (about 10^-5 to 10^-3); in unconfined aquifers it approximates specific yield (0.05 to 0.25) and feeds Theis drawdown analysis.

Confined aquifers are bounded by aquitards and store water under pressure, so pumping lowers the potentiometric surface with little drainage; unconfined aquifers have a free water table and dewater pore space, giving them much larger storage.

The three-dimensional drawdown zone around a pumping well; its radius grows with time under the Theis solution until it reaches a recharge or barrier boundary. Overlapping cones from neighboring wells cause well interference and can cut yields below design.

In coastal aquifers, denser seawater forms a wedge beneath fresh groundwater; excessive pumping lowers heads below the Ghyben-Herzberg equilibrium, drawing saltwater inland. Control depends on managing pumping and maintaining freshwater heads above sea level.

R = 1 + (bulk density / porosity) x distribution coefficient, and it describes how sorption slows a contaminant relative to groundwater velocity. Non-reactive tracers have R of 1, while strongly sorbing contaminants lag by orders of magnitude.

Shear strength equals cohesion plus effective normal stress times the tangent of friction angle. Effective stress controls strength; raising pore water pressure lowers effective stress and can trigger slope or foundation failure even when total stress is unchanged.

Effective stress equals total stress minus pore water pressure, and it is the stress carried by the grain skeleton. Because shear strength and settlement depend on effective stress, pore pressure changes (common during earthquakes) can cause failure without any change in total load.

Saturated loose sand loses strength when shaking raises pore pressure until it equals total stress, dropping effective stress near zero. Liquefied sand behaves as a fluid, causing settlement, lateral spreads, and foundation failure; mitigation densifies the sand or drains pore pressure.

Blows counted for the last 12 inches of an 18-inch drive using a 140-pound hammer falling 30 inches. N correlates empirically with relative density, friction angle, and liquefaction resistance, but corrections for overburden pressure and energy ratio are essential.

Both classify rock mass quality: the RMR (Bieniawski) sums ratings for strength, RQD, joint spacing, joint condition, groundwater, and orientation, while the Q-system (Barton) uses RQD, joint set number, roughness, alteration, water, and stress. Cross-compare them; neither replaces in-situ observation.

Rotational slumps follow curved slip surfaces in cohesive soil; planar failures follow weak planes; wedge failures occur at intersecting joint sets; toppling develops where joints dip steeply into the slope. Identifying the controlling mechanism dictates the right analysis.

Rock bolts are passive support that builds a compression ring by mobilizing the rock's own strength; steel sets and concrete liners are active support that carries load directly. Good ground allows passive methods, while poor ground or high stress may require combined support.

Dense sulfide or oxide minerals crystallize and settle in layered mafic intrusions, forming chromite and platinum-group-element reefs such as those in the Bushveld and Stillwater complexes. Cumulate layering controls geometry, so stratigraphic position within the intrusion guides exploration.

Large, low-grade deposits associated with porphyritic intrusions, featuring disseminated and veinlet sulfides in stockwork fractures. Alteration zoning (potassic, phyllic, argillic, propylitic) is the key exploration guide, and induced-polarization and resistivity surveys detect the conductive sulfide halo.

Both are stratiform massive sulfide deposits, but SEDEX forms from seafloor hydrothermal brines in sedimentary basins (often lead-zinc), while VMS forms in submarine volcanic settings (copper-zinc-lead). Host-rock assemblage and tectonic setting distinguish them and shape exploration models.

Oxidation of pyrite and other sulfides in exposed mine waste generates sulfuric acid and dissolved metals, often persisting long after mining ends. Control depends on limiting oxygen and water contact, adding alkaline amendment, and collecting and treating drainage.

A resource is the naturally occurring material that can be economically extracted (measured, indicated, inferred); a reserve is the economically mineable part of a demonstrated resource. Classification shifts with commodity price, technology, and regulation, so reserves can grow or vanish without any new drilling.